US2567710A

US2567710A - Accelerating composition

Info

Publication number: US2567710A
Application number: US775959A
Authority: US
Inventors: Rutherford B Hill
Original assignee: Monsanto Chemicals Ltd
Current assignee: Monsanto Chemicals Ltd; Monsanto Chemical Co
Priority date: 1947-09-24
Filing date: 1947-09-24
Publication date: 1951-09-11
Anticipated expiration: 1968-09-11

Description

Patented Sept. 11 1951 Rutherford B.' Hill, lflitro, QWgYa assignor to Monsanto Chemical Company,ESt. Louis, M0,, .a

corporation of Delaware No Drawing. Application (September 24, '194'1, Serial No. 775,959

10 Claims. (61. 260-3065) The present invention relates to new compositions of matter and moreparticularly to accelerators and curatives for the vulcanization of a rubber or a rubber containing material. In addition, the invention relates to the process of vulcanizing a rubber and to the vulcanized rubber productsobtained with the aid of the new accelerators.

v Thiazole sulfides vare widely used accelerators in the manufacture of rubber articles. For example, 2,2'-dithio bis benz'othiazole is a useiul accelerator; but it, is a highj'meltingsolid diii'icult to disperse in a rubber andhas a very objectionable tendency to'cake onthe roll and adhere thereto. Langenbeck and Rheim, Kautsc'huk;l2, pp. 156-159 lM36),..have:demonstrated-that fusion of a thiazolesulfide and sulfur lowers the melting point of the former sharply. Investigation of these compositions revealed that incorporation into the rubbercould be accomplished much more quickly andeasily than with the pure thiazole sulfides. On theiotherlian'd,'the physical properties of the fusion products irom the standpoint oi'shipping, handling, removing from the container, etc. were so objectionable as to preclude their use as commercial accelerators. They are soft sticky pastes at room temperature.

An object of this invention is to provide accelerating compositions which maybe quickly and uniformly incorporated into a rubber. A more particular object of the invention is to provide accelerating compositions which either melt or soften'during the processing of the rubber. Another object is to provide thiazole accelerators in improved physical form. A particular object .is to improve the physical properties of fusion products of thiazole sulfides and sulfur; Other and further objects will inpart be apparent and in part particularly pointed out in the detailed description following.

In accordance with the present invention it has been discovered that treatment of composite heat fusion productsof 'thiazole sulfide accelerators and sulfur with a baseprovides low melting compositions which quickly and uniformly disperse into rubber'at processing temperatures and at,

the same time possess Satisfactory physical properties at :room temperature. The base may beadded prior to, during, or'after the fusion.

While chemical reaction between thiazole sulfides and sulfur has been postulated, this invention is not limited to any theory of the presence or absence of chemical modifications. The acceleratingxpr pfirti s' of the fusion products are closely. .comparableysto that which would be expeotedirom (their thiazole sulfide content. 7

Apparently'the nature of the base employedis i not; critical. ='I-he' alkali metal hydroxides, the

alkaline 'earth metal hydroxides, ammonia, organicibasesQpreferabIy organic bases stronger than ammonia such as :cyclohexylamine, .b.enzyl amine, piperidine, ethyl amine, diethyl amine, methyl amine, dimethyl amine, morpholine, methyl cyclohexylamlne,and the like may be used. A small amount of the base is suflicient. In general, 0.l %-l.0 based'on the tamr'weigm of the composition iss'atisfactory. For example,

0.1% of ammonia added toiafusion inixtfire'bf' equal parts by weight .of sulfur and" dithio-fbis benzothiazole gave a "hard --:grindable product melting at 97 C. On the other hand xlessithan 0.1% had no noticeable efiect andlprovide'd soft products which were not grindable. cases 0.5% by weight of the base is about the optimum concentration of base.

The proportion of f-sulfu-r can-vary widely; Compositionscontainingless than 50 ya-sulfur are soft and sticky andtreatmentwi-tha base depresses the melting point still further so far" that they liquefy at temperatures only --slightly' above room temperature and therefore may be easily melted-and 'handledas liquids. -I-t is preferrd however to employ compositions' containing at least 5 0% sulfur. These compositions are-hard grindable solids after treatment with a base although they-soften and liquefy 'at the temperatures reached during processing of therubber.

The table below shows-the infiuenceof varying the proportion of dith-iio -bis' -ben'zothiazole and sulfur, either in the presence-or absence-of ammonia. Fusion products were prepared in'wliich the gram atoms ofsulfupper gram moi of-disulfide were 16, 14, 12, 10.4, 10, 8, 6.9, 6, 4, 2.6 and 2 respectively. Fusion was carried out by heating the ingredients until a clear melt was obtained The compositions were cooled and then placed on-asteam bath and their physical condition at 10. noted. The preparation of the fusion .products was then repeated, but in this Lcasethere was added'to the melt-0.5% based on the -'total composition of 28% ammonium hydroxide. The fusion mixtures were then allowed "to "cool, their physical conditionnoted;and"theirmelting points In most 3 determined. All of the compositions treated with ammonia and which contained at least 50% sulfur were hard friable products at room temperature.

The stocks so compounded were vulcanized by heating in a press for difierent periods of time at 142 C. The physical properties of the cured products are set forth in the table following.

Table I Dithio Without ammonia, Physical condition After ammonia b bis sulfur of fusion product atgreameit, M P BHZO- YS 011- thiazole, Per Cent dition at room 0 Per Cent Room Temperature 95 0. temperature 39.3 60.7 soft sticky solld liquid hard solid..- 104 42.5 57.5 do do do 107 46.4 53.6 (in do (in 109 50.0 50.0 n 00 108 51. 0 49. 0 do --rio soft solid 61 50.5 43.5 do 50 00.0 40.0 do solid-liquid--. --.--do 46 63.4 36.6 rin (in do 47 72.2 27.8 do do (in 43 80.0 20.0 do. on on 44 83.8 16.2 do soft solid .do 46 7 Table III While any base appears to accelerate the hard- Modulus of Elasenmg, there is some variation in their efiectiveticity in lbs lin-fl D ness. For example, equal amounts by weight of stock gj aLewngatwnS 2? dithio bis benzothiazole and sulfur were heated Mins. lbs/in? Per Cent to form a clear melt and then treated with 0.25% 30 300% 500% based on the total combined weight of the following bases. The compositions were then coolec 90 123 186 860 and their physical properties noted. 15 150 100 243 506 283 523 680 720 22 2. .2 as 1,, 1,200 oso Table H 453 986 1,600 730 666 1, 310 Y 1, 520 563 00 030 1, 386 1. 993 683 Base Condition after cooling I m Stocks were compounded comprising None soit sticky. I NaOFT soft, becoming hard and brittle after 48 hours. Stock 3 H 4 N11. hard and brittle. Piperidine- Do. Cyclohexylamme.-- D0. Parts by Parts by weight weight 4 5 Smoked sheet rubber 100' mcjoxugeln 5 5 at on a 45 45 Into a container of suitable capacity fitted with Stearic acid. 3 3 an agitator there was charged pounds of sulg gf ffff fff fff j'fff n g g 55 fur. The sulfur was melted and then 125 pounds N-eyolollexyl2-benzothiazola sulfenamide- 0.3 0:3 of 2,2 dithio bis benzothiazole was added at 110- 50 gg 0. 5 112 C. over a period of about 40 minutes while I stirring. The mixture was then heated to 148 C, and 5 pounds of a 25% aqueous caustic soda solution added gradually. The temperature dropped to 124 C. as the water evaporated but was then gradually brought up to 138 C. About 50 minutes was required for the addition of the caustic and heating to 138 C. The melt was then poured out into pans and allowed to 0001. After 18 hours the material had hardened considerably and after 48 hours was hard and brittle so that it could be finely pulverized. The pulverized product is identified as Accelerator A in the stock below.

The stocks were milled at 95 C. at which temperature Accelerator A softened and dispersed readily into the rubber whereas 2,2'-dithio bis benzothiazole tended to cake on the rollsinstead of going into the rubber. The compounded stocks were cured in the usual manner by heating in a press for different periods of time at 144.5" C. The physical properties of the cured rubber products are set forth below:

Table IV Stocks were compounded comprising Md11l18 i ticity in lbs/1n. 65 Cure at elongations Tensile'at Ultimate Stock Tune in of Break, in Elongation, I Mins. lbs/in. Per Cent W 1 2 300% 500% i? 2: i338 i 5 4.11 705 83 33 21 30 1. 450 of 240 4, 450 050 zinc mm 30 1, 420 3, 180 4, 040 050 fg g ggff arson-arc s v Into'fa container of suitable capacity there was "charged 3923 parts by weight 'of 2,2'-'dith'o bis benzothiazole and 60.? parts by weighto sulfur. The mixture was heated -uritil-a clear inelt was formed and then-0. 5 part by weight of 28% ammonium hydroxide added, and the melt allowed tocoolto room temperature. A hard .griiidable "sblid wasformed designated accelerator'B in the following'stocksz 1 Stock 5 6 Parts by Parts by weight weight GR-S rubber 100 100 Carbon black 40 40 Zinc oxide 3 3 Hydrocarbon softener 8 8 Bulim- 2. 32 0. 5 2,2 dithio bis benzothiazole 1. l8 Accelerator B 3.0

Accelerator B melted on the bank of the stock during mixing. The compounded stocks were cured by heating in the usual manner for different periods of time at 142 C. The physical properties of the cured products are set forth below:

The accelerating compositions of this invention are useful in the vulcanization of sulfur vulcanizable rubbery materials generally. Suitable rubbers comprise india rubber, reclaimed rubber, balata, gutta percha, butadiene-1,3 polymer, copolymer of butadiene-1,3 and styrene, copolymer of butadiene-V1,3 and acrylonitrile, and other sulfur vulcanizable rubbery products whether natural or synthetic.

The present invention is not limited to the specific examples herein set forth of the preparation and use of the preferred accelerators. The procedure for the preparation of the fusion products may be varied as will be apparent to those skilled in the art to which the invention pertains. While the use of the new accelerators has been described by references to particular formulations, other ratios of the compounding ingredients than those mentioned in the examples as well as other well known fillers, pigments, and the like may be employed in the production of various types of rubber compounds. Where desired basic activating accelerators may be employed in conjunction with the fusion products, as for example diphenyl guanidine, di-o-tolyl guanidine, thiocarbanilide, hexamethylene tetramine, para phenylene diamine, anhydro formaldehyde aniline, diphenyl guanidine phthalate, triphenyl guanidine, butylaldehyde aniline, di-

6 'butyl amine ole'ataand 'dicyclohexylamine ,oleate.

While sulfur may be added in addition 'to that presentinthe fus'ion product, the ratios in which the sulfur and accelerator are fused may be varied so as to avoid the-independent addition of either ingredient. For example, in compounding a stock calling for 3 parts of sulfur and 1 part of 2,2'-dithio bis benzothiazole, the sulfur and accelerator may with advantage be replaced by 4 parts of a fusion mixture of 3 parts ofsulfur and lpart o'f 2,2'-dithio bis-benzothiazole treated with abase as described herein. Thus, the invention contemplates replacing the usual sulfur and thiazole sulfide combinations with preformed composite fusion products fused in any of the ratios these ingredients are separately employed.

Instead of 2,2'-dithio bis benzothiazole other thiazole sulfide accelerators may be fused with sulfur, as for example 2,2 dithio bis 4,5-dimethyl thiazole, 2,2-dithio bis 4-ethy1 thiazole, 2,2-dithio bis 4-phenylbenzothiazole, 2,2'dithio bis methylbenzothiazole, 2,2-dithio bis fi-phenylbenzothiazole and 2,2'-dithio bis chlorobenzothiazole.

The invention is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. A vulcanization accelerator and curative prepared by treating with a 0.1 %-l.0% of a base the composite heat fusion product of a 2,2-dithio bis thiazole accelerator and sulfur.

2. A vulcanization accelerator and curative prepared by treating with 0.1%1.0% of a base the composite heat fusion product of a 2,2-dithio bis arylenethiazole accelerator and sulfur.

3. A vulcanization accelerator and curative prepared by treating with 0.1%-1.0% of a base the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur.

4. A vulcanization accelerator and curative prepared by treating with 0.1%-1.0% of a metal hydroxide the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur, the proportion of sulfur by weight being at least equal to that of the 2,2'-dithio bis benzothiazole.

5. A vulcanization accelerator and curative prepared by treating with 0.1%-1.0% of an alkali metal hydroxide the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur.

6.. A vulcanization accelerator and curative prepared by treating with 0.1 %-1.0% of ammonia the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur.

7. A vulcanization accelerator and curative prepared by treating with 0.1%1.0% of ammonia the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur, the proportion of sulfur being at least equal to that of the 2,2-dithio bis benzothiazole.

8. A vulcanization accelerator and curative prepared by treating with 0.1%-1.0% of an organic base the composite heat fusion product of 19119 equai pfdp'oitions by weight of 2,2'-dithlo'- Number Name Date bis benzothiazole andsulfur. v V} 2, 0 S y 1939 RUTHERFQRD B.- HILL. 2,262,398 Jones NOV. 11, 1941 ED 2,386,595 Jansen .1 Get. 16, 1945 v Th f n i n f d the 5 Y FOREIGN PATENTS file 0ef t1is0v;/)a%in1e erences are 0 rgcor 1 n Number Country Date, 504,583 7 Great Britain Apr. 2'7, 1939 UNITED STATES PATENTS Number Name H 6 Dat 10 1,544,687 Sebrell July '7,v 1925 1,926,740 vClapson Vet a1. Sept. 12, 1933 OTHER REFERENCES Kautschuk, v01. 12, of 1936, pages 156-159.

Claims

1. A VULCANIZATION ACCELERATOR AND CURATIVEE PREPARED BY TREATING WITH A 0.1%-1.0% OF A BASE THE COMPOSITE HEAT FUSION PRODUCT OF A 2,2''-DITHIO BIS THIAZOLE ACCELERATOR AND SULFUR.